1. Field of the Invention
The present invention relates generally to transportable apparatus for conveying particulate materials, and particularly to a transportable conveyor system for handling great volumes of sand or other proppant material and discharging the same at uniform rates to blender apparatus which blend the proppant with various liquids so that the same may be pumped down into an oil or gas well as part of a formation fracturing operation.
2. Description of the Prior Art
Increasing technology and improved techniques have resulted through the years in the use of greater volumes and higher concentrations of proppant in hydraulic fracturing operations in the oil field. This increased use of proppant has created the demand for more dependable proppant handling equipment capable of moving large amounts of proppant from on-location storage to the blending apparatus with little or no spillage. The system must also provide a steady, even flow of proppant to the blender to prevent fluctuations, in concentration rates being pumped down into the well.
For many years, the prior art has included the use of belt conveyors for gathering proppant material from a plurality of sources such as fixed bins or transportable storage bins, and for delivering the proppant to a blending apparatus.
Additionally, separate transfer conveyors capable of being swiveled about a vertical axis have been utilized at the end of the primary conveyor in order to permit the flow from the primary conveyor to be transferred to a plurality of blending apparatus.
With the prior art apparatus, and with the apparatus of the present invention, the primary purpose of the proppant conveying system is to maintain a steady and sufficient flow of proppant to the blending apparatus.
It is in the blending apparatus where the correct proportions of proppant to liquid are determined, and this can only be done by maintaining a steady supply of proppant to the blending apparatus.
The particular blending apparatus utilized by the assignee of the present invention includes a feeding machine consisting of a plurality of screw conveyors. Thus, the job of the proppant conveying system is to keep the intake portion of the screw conveyors full so that the screw conveyors will always convey a full load of proppant. This is necessary because the blending apparatus calculates the volume of proppant based upon the speed of the screw conveyors and the assumption that the conveyors are fully loaded.
The intake portion of the screw conveyors itself may be thought of as consisting of a relatively small hopper.
The problem encountered in the prior art, and to which the present invention is particularly directed, is that the volume of this small intake hopper on the blending apparatus is very much less than the volume of material which at any one time is being carried by the sand conveying apparatus.
Also, the lag time between the placement of proppant material on the conveyor and the delivery of that material to the blender apparatus is significant, on the order of as much as twenty seconds, and the amount of material which the conveyor system transports during that lag time very much exceeds the volume of the small intake hopper on the blender apparatus.
To appreciate the problem encountered by the operator of the conveyor system, it must be appreciated that the conveyor system operator does not generally control the requirements of the blender apparatus, but instead must respond to the needs of the blender apparatus. His job basically is to observe the intake hopper of the blender apparatus and make certain it is always substantially full of proppant material, but also he of course does not want to overfill the intake hopper of the blender apparatus since that would result in a waste of proppant material.
The job of the conveyor operator through the years has become increasingly more difficult as the size of hydraulic fracturing operations has increased so that the rates at which proppant must be supplied to the blenders has accordingly increased.
The situation has reached the point where with prior art apparatus, it is very difficult for a human operator to repsond quickly enough to the situation he observes at the intake of the blender apparatus. When the demand for proppant at the blender decreases, it is difficult, if not impossible, for the human operator to stop the supply of proppant to the blender before overflowing the blender intake hopper. Similarly, the blender can quickly exhaust the small supply of proppant which it holds in its intake hopper before the human operator of the conveyor system can deposit proppant material on the conveyor and transport it by means of a conveyor to the blender apparatus.
Thus, the need has developed for a system which can smooth out or reduce fluctuations in the flow of proppant material to the blender apparatus, at relatively high flow rates of proppant material.
The prior art includes devices which have attempted to do this through the use of a surge bin located immediately adjacent the blender apparatus. In some instances, these surge bins have actually been comprised of an extension to the intake hopper of the blender apparatus.
Another prior art device has provided such a surge bin on the rear end of a transportable conveyor system, wherein the surge bin was designed to be located immediately above the intake hopper of a blender apparatus so that the contents of the surge bin were dumped directly into the blender apparatus.
Thus, although the prior art has contemplated the general problem addressed by the present invention, namely the provision of a proppant transport system which can handle relatively large volumes of material and which provides some means within the system for temporary storage of material being conveyed, there still has not prior to the present invention been provided a completely integrated transportable system which is capable of receiving proppant material from a plurality of sources, temporarily holding that material in a surge bin contained within the transportable system, and then discharging the proppant material from the surge bin and conveying the material to a variable discharge point relative to the surge bin.